In recent years, the continued miniaturization of large scale integrated circuits (LSI) has lead to demands for techniques capable of processing ever finer structures. In response to these demands, a method has been disclosed for forming a very fine pattern using a phase-separated structure that is formed by the self-assembly of a block copolymer containing mutually incompatible polymers bonded together (for example, see Patent Document 1).
In order to utilize this type of block copolymer phase separation, a self-assembled nanostructure formed by microphase separation must be formed within only a specific region, and must be oriented in the required direction. In order to achieve this positional control and orientation control, methods such as graphoepitaxy, which controls the phase-separated pattern using a guide pattern, and chemical epitaxy, which controls the phase-separated pattern based on differences in the chemical state of the substrate, have been proposed (for example, see Non-Patent Document 1).
Methods for selectively removing a specific polymer region from the nanophase-separated structure of a block copolymer can be broadly classified into liquid phase methods and dry methods (for example, see Patent Document 2). A dry method (dry etching) is a method in which a reactive gas is blown onto the nanophase-separated structure, and selective removal is achieved based on the difference in the polymer decomposition rates in the presence of the dry gas. On the other hand, a liquid phase method (solution etching) is a method in which following selective decomposition, where necessary, of a polymer in a specific polymer region within the nanophase-separated structure, the nanophase-separated structure is immersed in a developing solution, and the specific phase portion of the structure is dissolved preferentially. In solution etching, a developing solution having an aqueous solution base is generally used. This is based on the high solubility in aqueous solutions of the substances thought to be formed upon polymer decomposition.